I'm an A-Level student, studying Further Maths. We've chosen the Further Mechanics as our optional module of the course.
Further Mechanics, unfortunately, is not making a lot of sense to me, because a lot of it isn't clicking whatsoever. I have two questions which I'm asking here because they also come from the physics A-Level course (I have friends who do it, and in retrospect I probably should have too).
Here are my questions:
- The equation for power is: power = driving force • velocity. While I understand how this equation is derived, but this is what I don't understand: if the velocity of an object is affected by the forces acting in the direction of its motion and in the opposite direction to its motion, why do we use the driving force, i.e. the force acting in the direction of motion without the resistant forces, as opposed to the resultant force?
- Say we have an object that moves to the right across a rough horizontal surface. The force R is the normal force that acts against the force of gravity. Why is it that, as opposed to using the force of gravity as a source of resistance, we commonly express the resistant force against the direction of motion as μR, where μ represents the coefficient of friction? Surely it would make more sense to use the force of gravity, the thing pushing it further to the ground, than to use the normal force? Of course in many examples they'll be the same, and so it wouldn't make a difference. But why opt for the normal force going up, as opposed to the gravitational force weighing it down?
I do apologise if any of what I've asked is ambiguous or vague, this is a very confusing area of maths for me.